This invention relates to power transmission devices of the rotary-to-linear motion converting type. Such devices are widely used wherever the input power is furnished rotationally such as by an electric motor or the like and where the desired output is in linear directions, and are known as "actuators". However, the present invention has particular application to systems for so-called "climate control" of atmospheres within confined areas, and/or other control functions wherever computer or microprocessor controlling agencies having limited power output capabilities are employed. This invention provides an improved "harmonic screw" type actuator wherein rotary motion of the power input component is converted into linear motion of the output component by means of a strain wave imposed upon a flexible sleeve member of the assembly, which is flexed into intermittent screw engagement by a member which is motor-driven to rotate relative to the periphery of the flexible sleeve; thereby causing progressively advancing/retreating interengagements of thread-like surfaces formed on the axially stationary and axially movable components of the system. Prior art devices of this general type are disclosed for example in U.S. Pat. Nos. 2,906,143; 2,943,508 and 2,979,964, and are employed to operate levers/arms/cranks/slides or the like, such as for opening and closing doors/gates/slides/butterfly damper valves, etc.; and wherever push-pull power outputs are required.
An object of the present invention is to provide for a harmonic screw actuator of the type aforesaid an improved "fail-safe" control arrangement such as will automatically operate devices attached to its power output device. This feature is of particular importance such as for example in the building industry wherein it is required to provide for automatic closing of outside air inlet ducts and simultaneous openings of air outlet ducts, such as in the case of a fire in order to prevent fresh air inlet fannings of the fire and ready escape of smoke from within the building. Another object is to provide a rotary-to-linear actuator as aforesaid which is of high capacity yet of light weight and of simple construction; and which provides for precision positioning with or without feedback. The actuator of the invention eliminates the need for gear reductions such as are normally required in typical screw type actuators; and therefore is of much more simplified and less costly construction.